A power supply module such as an Alternating Current (AC)/Direct Current (DC) rectifier module and a DC/DC converter has been widely applied to the fields of communication, computer, automobile and home appliance. A DC bus in the power supply module circuit is generally connected to an electrolytic capacitor and other electronic devices. When the power supply module connected to a power supply is started at the first time or when the power supply module is hot plugged on a power supply system, since a voltage on the DC bus in the power supply module does not necessarily reach a voltage resulted from an AC input after being rectified or a voltage of a DC input, a big current shock will be caused to the electrolytic capacitor connected to the DC bus, and the big current shock will result in damage to the electrolytic capacitor and occurrence of electric arc in a connection terminal connecting the power supply system and the power supply module, which may damage the connection terminal.
For the above problems, there are two solutions in the prior art, one is that soft start of the DC bus is realized in a way of cooperating a structure of mechanical lock with long and short pins of a connector; and another is that the soft start of the DC bus is realized by connecting a current-limiting resistor connected in parallel with a switch device into the DC bus.
The first solution is as shown in FIG. 1 or FIG. 2, in which a current limiting resistor R1′ is connected in one of two DC buses (the one of two DC buses may be the DC bus connected to an input terminal Input1 or may also be the DC bus connected to an input terminal Input2 . In FIG. 1 and FIG. 2, the DC bus connected to the input terminal Input2 is taken as an example), the resistor R1′ is connected to a longer pin of the input terminals in the power supply module including the two DC buses. When the power supply module is plugged into a power supply system which has been powered on, it can make sure that the longer pin of the input terminals in the power supply module first makes contact with the power supply system which has been powered on, and consequently the capacitor C1′ between the two DC buses is charged via the current limiting resistor. The mechanical lock is then opened so that the power supply module is plugged into the right place completely. At that time, the longer pin connected to the resistor R1′ is disconnected from the power supply system, and a pin of the input terminals in the power supply module which is connected to the input terminal Input2 is connected to the power supply system, and is connected to a pin in the output terminals of the power supply system which is in contact with the longer pin connected to the resistor R1′ before the mechanical lock is opened. A difference between FIG. 1 and FIG. 2 is that signal input to the input terminal Input1 and the input terminal Input2 in FIG. 1 is a DC signal, and signal input to the input terminal Input1 and the input terminal Input2 in FIG. 2 is an AC signal, and the AC signal is converted into a DC signal via an AC/DC rectifier. A DC/AC converter or a DC/DC converter connected in parallel with the capacitor C1′ is also included in FIG. 1 and FIG. 2. If the DC/AC converter is connected in parallel with the capacitor C1′ in FIG. 1 and FIG. 2, an AC signal is output from the two output terminals Output1 and Output2 in FIG. 1 and FIG. 2, and if the DC/DC converter is connected in parallel with the capacitor C1′ in FIG. 1 and FIG. 2, a DC signal is output from the two output terminals Output1 and Output2 in FIG. 1 and FIG. 2. A disadvantage of this solution is that, in this solution, first, the applying of delay is dependent on the structure of mechanical lock added to the power supply module, and since a duration of the delay is dependent on the capacitor C1′ and the current limiting resistor R1′, if the operation is too fast, there is a high difference between the voltage on the DC buses and the input DC voltage or the voltage of the DC signal obtained from the input AC signal after being rectified, which may also result in a big current shock and consequently result in damage to the electrolytic capacitor on the DC buses, and may damage the connection terminal connecting the power supply module including the DC buses and the power supply system. Therefore, it is apparent that the power supply module having such a structure has a high requirement on the skill of the operator. In addition, if the power supply module has been plugged into the power supply system, a big inrush current will be generated when the power supply system is powered on, although which inrush current will not damage the connection terminal connecting the power supply module and the power supply system, but will damage the electrolytic capacitor on the DC buses.
The second solution is as shown in FIG. 3 or FIG. 4. In FIG. 3, a current limiting resistor R1′ being connected in parallel with a switch device 31 is connected to a DC bus connected to an input terminal DC+ or a DC bus connected to an input terminal DC− (in FIG. 3, the DC bus connected to the input terminal DC+ is taken as an example). In FIG. 4, a current limiting resistor R1′ being connected in parallel with the switch device 31 is connected in series with a branch circuit where a capacitor C1′ is located. Each of the DC buses in FIG. 3 and FIG. 4 receives a DC signal. When a power supply module including the DC buses shown in FIG. 3 or FIG. 4 is plugged into a power supply system that has been powered on or when the power supply system into which the power supply module is plugged is powered on at the first time, the capacitor C1′ in the DC buses is charged at first by the power supply module via the current limiting resistor R1′. When it is detected that a voltage on the DC bus reaches a predetermined value, the switch device 31 is closed (turned on) to short-circuit the current limiting circuit R1′ and a current flows through the switch device 31. In this way, the current flows through the current limiting resistor R1′ when the power supply module including the DC buses is powered on to start, and the current flows through the switch device during normal operation, thus realizing the purpose of soft start. Compared with the first solution, in the second solution, no big inrush current will be generated whether when the power supply module is hot plugged or the power supply system including the power supply module is powered on. However, the second solution has disadvantages as follows. When the hot plug is performed repeatedly and if the operation is performed fast, the voltage on the DC bus in the power supply module will drop slowly after the power supply module is unplugged from the power supply system, and the power supply module is plugged into the power supply system fast again before the voltage drops to a shut-down determination voltage or a determination voltage for opening (turning off) the switch device. Since there is a difference between the DC voltage output from the power supply system and the DC voltage on the DC buses of the power supply module, a big inrush current may be generated, which may damage the capacitor C1′ between the two DC buses and may damage the connection terminal connecting the power supply module and the power supply system.
In conclusion, in a case that the existing DC bus structure is employed, when the power supply module including the DC buses is hot plugged rapidly on the power supply system, a big inrush current may be generated, which may damage the capacitor between the two DC buses and damage the connection terminal connecting the power supply module including the DC buses to the power supply system.